1. Field of the Invention
The invention relates to a voltage calibration method for a rechargeable battery set, and particularly, to a voltage calibration method that calibrates the measured voltage of each battery cell via reducing the effect of internal resistance of each battery cell.
2. Description of the Prior Art
To supply sufficient voltage for equipments, a rechargeable battery set is usually composed of many battery cells serially connected with one another. Such combination of battery cells may well serve as the power source for notebooks, medical equipments, or equipments with high power consumption. Generally, the serially connected battery cells should be balanced in voltage as for the design of the rechargeable battery set. It is, however, highly possible that each battery cell may have different measured voltage detected by the control unit inside the rechargeable battery set, which is mainly caused by resistances from the wiring between the battery cells and the nickel rods attached to the battery cells at the ends of the battery set. Some techniques have been used in the prior art to balance the voltage of each battery cell inside the rechargeable battery set. These techniques substantially include two major types: cell voltage balance and cell capacity balance. Nevertheless, such voltage balance techniques are incapable of dealing with the internal resistances caused by the wiring and the nickel rods.
For example, in a rechargeable battery set having many battery cells serially connected with one another, the internal resistance of each battery cell may alter due to the layout of the battery cells. Secondly, the battery cells at the ends of the battery set commonly have higher internal resistances with respect to other battery cells because of the nickel rods. As with the influence of the internal resistances, the control unit may mistakenly determine the rechargeable battery set to be fully charged in charging process but the battery cells are actually far from fully charged. The control unit may also mistakenly learn that the battery set is already out of power in discharging process, while the battery cells do still have some power. This just make the rechargeable battery set provide less than its specified capacity, and incorrect charging/discharging process also seriously damages the life of the battery set.